Docs: Relax permission for merging PRs (refs eslint/tsc-meetings#20)

[btmills]

What is the purpose of this pull request? (put an "X" next to item)

[x] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

Please check each item to ensure your pull request is ready:

• I've read the pull request guide
• n/a I've included tests for my change
• I've updated documentation for my change (if appropriate)

What changes did you make? (Give an overview)

Following today's TSC meeting, added a note that committers may merge any PR that has been approved by a TSC member.

Is there anything you'd like reviewers to focus on?

The previous requirements for merging a PR without explicit TSC member approval haven't changed?

[mention-bot]

@btmills, thanks for your PR! By analyzing the history of the files in this pull request, we identified @nzakas to be a potential reviewer.

[eslintbot]

LGTM

[kaicataldo]

LGTM